# output.assetPrefix

- **Type:** `string | 'auto'`
- **Default:** [server.base](/config/server/base)

In [production mode](/config/mode), use this option to configure the URL prefix for static assets, such as a CDN URL.

`assetPrefix` affects the URLs of most static assets, including JavaScript files, CSS files, images, videos, etc. If an incorrect value is specified, you'll receive 404 errors while loading these resources.

This configuration is only used in `production` mode or `none` mode. In `development` mode, use [dev.assetPrefix](/config/dev/asset-prefix) to configure the URL prefix.

## Example

Setting `output.assetPrefix` will add the value as a prefix to the URLs of all static assets like JavaScript, CSS, images, etc.

- For example, setting it to a CDN address:

```ts title="rsbuild.config.ts"
export default {
  output: {
    assetPrefix: 'https://cdn.example.com/assets/',
  },
};
```

After the build, the URL of the JS bundle in the HTML file will be:

```html
<script
  defer
  src="https://cdn.example.com/assets/static/js/index.ebc4ff4f.js"
></script>
```

- Setting it to a relative path:

```ts title="rsbuild.config.ts"
export default {
  output: {
    assetPrefix: './',
  },
};
```

After the build, the URL of the JS bundle in the HTML file will be:

```html
<script defer src="./static/js/index.ebc4ff4f.js"></script>
```

## Default value

The default value of `output.assetPrefix` is the same as [server.base](/config/server/base).

When `server.base` is `/foo`, `index.html` and static assets can be accessed through `http://localhost:3000/foo/`.

It should be noted that when customizing the `output.assetPrefix` option, if you want static assets to be accessible normally during [Rsbuild preview](/guide/basic/cli#rsbuild-preview), `output.assetPrefix` should contain the same URL prefix as `server.base`. For example:

```ts title="rsbuild.config.ts"
export default {
  output: {
    assetPrefix: '/foo/bar/',
  },
  server: {
    base: '/foo',
  },
};
```

## Path types

assetPrefix can be set to the following types of paths:

- **absolute path**: This is the most common practice, which can be specific server paths like `/assets/`, or CDN paths like `https://cdn.example.com/assets/`.
- **relative path**: For example, `./assets/`.
- **'auto'**: Rspack will automatically calculate the path and generate relative paths based on file location.

:::tip
It's not recommended to set assetPrefix as a relative path like `'./assets/'`. This is because when assets are at different path depths, using relative paths may cause assets to load incorrectly.
:::

## Compare with `publicPath`

The functionality of `output.assetPrefix` is basically the same as the [output.publicPath](https://rspack.rs/config/output#outputpublicpath) config in Rspack.

Key differences from the native configuration:

- `output.assetPrefix` only takes effect in production mode.
- `output.assetPrefix` default value is the same as [server.base](/config/server/base).
- `output.assetPrefix` automatically appends a trailing `/` by default.
- The value of `output.assetPrefix` is added to the [process.env.ASSET_PREFIX](/guide/advanced/env-vars#processenvasset_prefix) environment variable (can only be accessed in client code).

## Dynamic asset prefix

Use the `__webpack_public_path__` variable provided by Rspack to dynamically set the URL prefix of static assets in JavaScript code.

See [Rspack - Dynamically set publicPath](https://rspack.rs/config/output#dynamically-set-publicpath).
